Network interface configuration files in CentOS, Fedora and other RHEL based Linux systems are located in /etc/sysconfig/network-scripts directory. It also contains the control scripts to enable or disable the interfaces.
For each network interface there is a corresponding configuration script which contains information specific to that particular interface. The interface configration file names are of the format ifcfg-<device name>. So ifcfg-eth0 will be the configuration file for network interface eth0, which is usually the first network interface card (NIC) in the system.
Network configuration files are updated when you make changes to the network using the Network Adminsitration Tool (system-config-network). Alternatively you can manually edit the configuration files for a NIC.
The most commonly used configuration parameters are :
DEVICE=<name>
<name> is the name of the device
BOOTPROTO=<protocol>
<protocol> can be none, bootp or dhcp
BROADCAST=<address>
<address> is the broadcast address
GATEWAY=<address>
<address> is the gateway IP address
HWADDR=<MAC-address>
<MAC-address> is the hardware address of the NIC
IPADDR=<address>
<address> is a static IP address assigned to the NIC
NETMASK=<mask>
<mask> is the netmask value
ONBOOT=<value>
<value> is yes for device to be activated at boot time or no if the device should not be activated at boot time
USERCTL=<value>
<value> is yes to allow non-root users to control the device or no if non-root users are not allowed to control the device
